Fiddle brake issues

[doddzee]

Hey guys ive got fiddle brakes on the rear of my new pajero but they are locked up hard. They move freely without any fluid in them but as soon as the system is bled the levers are unable to be moved. The rear brakes are not locked and work fine with the main braking system and seemed to be plumbed up correctly. The main line to the rear splits into the cylinder and then each line from the outlet of each cyliner runs off to the caliper. I cannot see anything in the lines which would be restricting the flow.

Any ideas on what could be wrong with them?

[Pedro]

Hey guys ive got fiddle brakes on the rear of my new pajero but they are locked up hard. They move freely without any fluid in them but as soon as the system is bled the levers are unable to be moved. The rear brakes are not locked and work fine with the main braking system and seemed to be plumbed up correctly. The main line to the rear splits into the cylinder and then each line from the outlet of each cyliner runs off to the caliper. I cannot see anything in the lines which would be restricting the flow.

Any ideas on what could be wrong with them?

post a photo of the setup, if the rear brakes are not locked then it must be a mechanical issue, are the cylinders moving over the full range, ie releasing the fluid, also the cylinders the hillman imp type, if so the fitting furtherest from the lever is inlet, and the one closet is line to wheel,

Cheers

Pedro

[doddzee]

Here it is, pulled one cylinder apart to see if there was anything going on there but it seems fine. The inlet comes to the tee peice and tees off the the inlet of the cylinder then the outlets run of to each individual caliper. When the system has been bled the lever only moves the cylinder about 2mm it is enough to lock the wheel when it is up on a jack but does nothing when driving. If you undo the outlet enough to release the fluid the cyliders move over their full range. The problem may be in the rear calipers but i would assume they would not work when applying the pedal if that was the case.

*edit*

Undoing the caliper bleed nipple wile pulling the lever allowes the cylinder to go its full travel so the problem is in the calipers. Are there some calipers which do not work with fiddles?

[mercutio]

what size cylinders are you using for the fiddles are you sure they are the correct size for the job

[doddzee]

what size cylinders are you using for the fiddles are you sure they are the correct size for the job

they are 3/4, pretty sure they are the hillman type but cant be 100% sure as i did not fit them.

[cool__bananas]

could they be rusted open or something?

[Heath]

Slightly off topic but curious as to how these work.

Im guessing the cylinders have a bypass some how for normal flow through them and when you push/pull on the lever they block the feed and apply pressure to one caliper. If that is the case then they would be relying on the small volume of fluid in the cyclinder to push the caliper pots closed. The volume of the cylinder doesnt look that big, maybe that is the problem (just not enough fluid volume)? Or is the bypass (or whatever) not working?

[turoa]

Slightly off topic but curious as to how these work.

Im guessing the cylinders have a bypass some how for normal flow through them and when you push/pull on the lever they block the feed and apply pressure to one caliper. If that is the case then they would be relying on the small volume of fluid in the cyclinder to push the caliper pots closed. The volume of the cylinder doesnt look that big, maybe that is the problem (just not enough fluid volume)? Or is the bypass (or whatever) not working?

there is no bypass. When using normal brakes the fluid passes through the cylinders normally and apply the brakes. When you pull on the lever they block off the inlet and force pressure through the outlet line.

The cylinders are not the issue. Alsmost every trials truck out there uses imp ones

[Heath]

Sweet just curious.

Sounds like a caliper issue then.

[Pedro]

When the system has been bled the lever only moves the cylinder about 2mm it is enough to lock the wheel when it is up on a jack but does nothing when driving.

How big are the rear calipers, from memory they are a little wee fellas, then 2mm travel on the master = 0.5mm travel on caliper, redo the pivot points for the cylinders, mine is set up with about a 12-1 ratio, 12mm of handle movement = 1mm of cylinder movement= shite load of force on rear caliper. i can lock up my wheels with 2 fingers on the wheel brake levers,
i have hillman imp cylinders driving the large 4 pot hilux calipers.

Pedro

[doddzee]

The Levers are pretty long so i didnt think its a leverage would be an issue.

[DieselBoy]

When i was setting mine up i had an issue with the system pumping its self up and locking the brakes on. That was due to the leavers not returning far enough to allow the cyclinders to open the flow through circut back up.


A possibility that just came to mind is that you/previous owner may have hooked the brake lines into the cyclinders the wrong way round. If they are round the wrong way, when you pull on the leaver you would be tring to compress the fluid back into the main master cyclinder. If the main brake pedal isn't returning all the way home, it may be that the main master cyclinder is locked off still, and you can't compress the fluid back into the reserviour(sp?) as it should(Thats only if the lines are around the wrong way and the pedal is adjusted wrong though).

Another thought aswell, have you bled the brakes up, and gone for a drive and tried loading up the independant brake leavers??

On a properly bled system, there is not a huge amount of movement in the leaver, its more related to the pressure applied to the leaver.

Also, the brakes on mine do strange things, you pull the leaver, the leaver moves a bit and locks the wheel, you release the leaver, and the leaver stays where it is, but as you have released the pressure on the leaver and in the brakeline, the wheel unlocks. Its not untill you put your foot on the brake again that the independant leaver/cyclinder pump up with fluid again and return to there proper spot. This is because the/my independant brake cyclinders don't have there own seperate reserviour i guess.

Anyways, i'm still thinking of more possibilities.........................

[doddzee]

When i was setting mine up i had an issue with the system pumping its self up and locking the brakes on. That was due to the leavers not returning far enough to allow the cyclinders to open the flow through circut back up.


A possibility that just came to mind is that you/previous owner may have hooked the brake lines into the cyclinders the wrong way round. If they are round the wrong way, when you pull on the leaver you would be tring to compress the fluid back into the main master cyclinder. If the main brake pedal isn't returning all the way home, it may be that the main master cyclinder is locked off still, and you can't compress the fluid back into the reserviour(sp?) as it should(Thats only if the lines are around the wrong way and the pedal is adjusted wrong though).

Another thought aswell, have you bled the brakes up, and gone for a drive and tried loading up the independant brake leavers??

On a properly bled system, there is not a huge amount of movement in the leaver, its more related to the pressure applied to the leaver.

Also, the brakes on mine do strange things, you pull the leaver, the leaver moves a bit and locks the wheel, you release the leaver, and the leaver stays where it is, but as you have released the pressure on the leaver and in the brakeline, the wheel unlocks. Its not untill you put your foot on the brake again that the independant leaver/cyclinder pump up with fluid again and return to there proper spot. This is because the/my independant brake cyclinders don't have there own seperate reserviour i guess.

Anyways, i'm still thinking of more possibilities.........................

The inlet and outlet are definatly plumbed up the right way, ive had them apart a dribbled fluid into them and it comes out the front when you compress the cylinder.

Yes the brakes have been bled and i was testing them out yesterday and no matter how hard you pulled it would not lock. Ended up bending one of the levers.

May strip the calipers down and see if that makes a difference.

[DieselBoy]

Well, they way it makes sense to me is that unless you rear brakes are dragging or locking on, or not working at all, then your problem is not with the caliper.

As i'm sure you have done, jack a wheel off the ground spin it by hand, then press the brake pedal, if the wheel stops, and rotates easily once you have released the pedal, then the calipers sweet. All there is in there is a piston and a couple of seals. If the piston was so tight that you couldn't move it with the independant brake leaver, the brake on that side would be dragging like a bitch and you would struggle to turn the wheel by hand!!!!!

But from your other posts, its about the last place to go looking i guess, like you said, undo the bleed screw at the caliper, actuate the independant leaver and it pumps fluid out.

[doddzee]

As i'm sure you have done, jack a wheel off the ground spin it by hand, then press the brake pedal, if the wheel stops, and rotates easily once you have released the pedal, then the calipers sweet. All there is in there is a piston and a couple of seals. If the piston was so tight that you couldn't move it with the independant brake leaver, the brake on that side would be dragging like a bitch and you would struggle to turn the wheel by hand!!!!!

Yip you are right, have done that. It seems like the last place to look so will try that before i change the lever set-up though im not convinced the problem is there as both levers are the same you would think that if it was the calipers one may work better than the other.

[DieselBoy]

Your leavers are fine, ,mine are waaaaaay shorter and work fairly well :




One other thing that occurred to me, is that in the photo below, the rod's running into the cyclinders are not aligned correctly ie, if the cyclinders are mounted horizontally, then the rod's should go horizontally, which it looks like they don't quite do.

If you try to load up those rods and they are not aligned correctly, they binde(sp?) on the cyclinder body (i had that problem due to sloppy tolerances on my linkages).

Perhaps try getting the nice and straight into the cyclinder and see what happens under load.



Still thinkin though.....................

[doddzee]

Perhaps try getting the nice and straight into the cyclinder and see what happens under load.
Still thinkin though.....................

Cheers for the ideas DB, tried that one too. I packed out the top and had it straight. It didnt help either. The end of the shaft is spherical so the alighnment doesnt seem to matter too much.

Bloody things are doing my head in.


Think i need to go over the hole system again and see what i can find, its probly something simple im missing.

[Pedro]

The Levers are pretty long so i didnt think its a leverage would be an issue.

looking at the setup it looks like the ration is about 4 to 1 no where enough to get good lock up, need to get lower pivot point and cylinder closer to gether , mine is like 30mm apart, yours looks closer to 80 or 90mm

Cheers

Pedro

[doddzee]

Do you have any pics of your set-up pedro so i can compare?

[skid]

Do you have any pics of your set-up pedro so i can compare?

somewhere, I have pics of the set up on orange

will dig them out

I'm not sure what the cylinders cost and it may be a cost you wont want to spend, but is it feasible to just buy new cylinders and slap them in to see if the other ones are shot.

seeing how the rest of the truck looks like it spent a lot of time outside, the fiddles may have got too much water in them.

right wheres those pics of mine

[skid]

found them, but they weren't as good as I thought they were.

you may find them useful but probably not.

anyway here they are..........................








maybe send a PM to Sig, as he has rear wheel brakes or anyone else you can think of that has them set up similarly.

just a thought

[doddzee]

Cheers Skid, Ive stripped the cylinder down and its like new. The surface rust looks alot worse in the pics.

Ill double check the calipers and if they still look sweet ill change the mounts.

[tpft]

remeber your main brake system runs threw a vaccum booster, while thease don,t.
i would think that as above even more mechanical advantage over the brake cyclinder would help.

Depends a lot on condition of rear pads and disc,s as well, all the clamping force in the world may not help if the surface is scored up or pads are glazed etc.
mine are on front, and even after truck has been sitting a while it takes a few good pulls to clean the disc,s and get a wheel to lock.
i guess its not lsd of course
any rubber hoses that are in the line, can swell and lose vaulable clamping force as well.

i just checked on mine, and brake cylinder rod only depresses a few mm to lock brake, lever moves like 100mm or so
move mounting point of rod down as much as possible, they will give u more mechanical advantage and more clamping force and feel

[sig]

make sure that the piston can return all the way to its stop .i would look at your ratio .approx 35mm from pivot centre to centre is a pretty good guide (this is what brian uses as his measurement)my levers are 500mm long and work ok ! but i,m gunna change the pivot point from 45mm (current) to about 35 and try that